Methods for thinning semiconductor substrates that employ support structures formed on the substrates

ABSTRACT

A support structure for use with a semiconductor substrate in thinning, or backgrinding, thereof, as well as during post-thinning processing of the semiconductor substrate includes a portion which extends substantially along and around an outer periphery of the semiconductor substrate to impart the thinned semiconductor substrate with rigidity. The support structure may be configured as a ring or as a member which substantially covers an active surface of the semiconductor substrate and forms a protective structure over each semiconductor device carried by the active surface. Assemblies that include the support structure and a semiconductor substrate are also within the scope of the present invention, as are methods for forming the support structures and thinning and post-thinning processes that include use of the support structures.

BACKGROUND OF RELATED ART

1. Field of the Invention

The present invention relates to structures for supporting semiconductorsubstrates during and following thinning thereof. More specifically, thepresent invention relates to support structures that are configured toentirely cover at least the outer peripheral portions of the activesurfaces of semiconductor substrates to impart the semiconductorsubstrates with some rigidity following thinning thereof.

2. Background of Related Art

Since its inception, the trend in electronics has been to developdevices of ever-decreasing dimensions and ever-increasing capabilities.In order to drive these trends, semiconductor device manufacturerscontinually develop new technologies to put more processing power, morememory, and more ancillary functionality into the same or smalleramounts of space.

One of the approaches that has been taken for reducing the size ofsemiconductor device packages or for facilitating the incorporation ofmore semiconductor dice into packages of a standard size has been toreduce sizes of the various package features, including the wire bondheights, the thicknesses of adhesive layers, the thickness of packagingmaterial which covers the package components, and the thicknesses of thesemiconductor dice themselves.

The thicknesses of semiconductor dice may be reduced prior tosingulation thereof from a semiconductor substrate, typically in theform of a silicon wafer, by reducing the thickness of the entiresemiconductor substrate. This is typically done by so-called“backgrinding” processes, which include mechanical or chemical removalof material from the back side of the semiconductor substrate and, thus,from the devices, or dice, that have been fabricated on the opposite,active surface thereof.

State-of-the-art backgrinding processes are useful for reducing thethicknesses of 200 mm diameter silicon wafers, which are typically about728 μm thick, and 300 mm diameter wafers, which are typically about 800μm thick, to as thin as about 50 μm. When the thickness of asemiconductor substrate is reduced, however, the semiconductor substratebecomes less robust. For example, when the thickness of a 200 mmdiameter silicon wafer is reduced to about 230 μm or less, it becomespliable and is prone to sagging when positioned on an edge or when anedge thereof is handled. As a consequence of the reduced robustness ofthinned semiconductor substrates, the semiconductor devices that havebeen fabricated thereon are more likely to be damaged when thinnedsemiconductor substrates are handled or packaged.

Moreover, when semiconductor substrates are thinned, they are typicallysecured, in active surface-down orientation, to a carrier, such as avacuum chuck. While the semiconductor substrate may be adequatelysecured to the carrier, the active surface of the semiconductorsubstrate may not be completely sealed from chemicalbackgrinding/polishing agents or particles of removed material. Thus,material may be removed from the active surface of the semiconductorsubstrate or the active surface may become undesirably contaminated.

Accordingly, there are needs for structures and methods for supportingsemiconductor substrates and for sealing the active surfaces thereofduring and following thinning thereof.

SUMMARY OF THE INVENTION

The present invention includes a support structure, or carrier, forsemiconductor substrates. The support structure is configured to bedisposed upon an active surface of a semiconductor substrate and tostructurally support and impart rigidity to at least an outer peripheralportion of the semiconductor substrate.

In one embodiment, the support structure comprises a ring which coversonly the outer peripheral portion of the active surface of thesemiconductor substrate. An outer peripheral edge of the ring extendssubstantially to or beyond an outer peripheral edge of the semiconductorsubstrate. An inner peripheral edge of the ring laterally surrounds aninterior portion of the active surface of the semiconductor substrate,on which semiconductor devices have been fabricated. Thus, thesemiconductor devices are laterally within the inner peripheral edge ofthe ring.

Another embodiment of the support structure includes an outer peripheralsection which covers the outer peripheral portion of the active surfaceof the semiconductor substrate, as well as an interior section whichcomprises a plurality of protective structures for each of thesemiconductor devices that have been fabricated on the active surface ofthe semiconductor substrate. The outer peripheral and interior sectionsof the support structure may be integral with one another. Thethicknesses of these sections may be substantially the same as ordifferent from one another.

In another aspect, the present invention includes semiconductorsubstrates with support structures that incorporate teachings of thepresent invention on at least portions of active surfaces thereof.

The present invention, in another aspect thereof, also includes methodsfor forming support structures on and securing support structures to theactive surfaces of semiconductor substrates. In one embodiment of such amethod, a support structure may be formed on an active surface of asemiconductor substrate by selectively consolidating regions of a layerof an unconsolidated material that has been applied to or otherwiseformed over the active surface. In another embodiment, a supportstructure of the present invention may be molded onto an active surfaceof a semiconductor substrate. In yet another embodiment, a preformedfilm may be applied and laminated to an active surface of asemiconductor substrate, and then so-called “subtractive” processes maybe used to form a support structure therefrom.

Additionally, the present invention includes methods for thinning andprocessing semiconductor substrates while support structures thatincorporate teachings of the present invention are secured to activesurfaces thereof. The present invention also includes methods forremoving support structures of the present invention from semiconductorsubstrates.

Other features and advantages of the present invention will becomeapparent to those of ordinary skill in the art through consideration ofthe ensuing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which depict exemplary features of various aspects ofthe present invention:

FIG. 1 is a top view of an exemplary semiconductor substrate, depictedas a wafer, which is shown as including a plurality of semiconductordevices on an active surface thereof;

FIGS. 2 and 2A are top views of the semiconductor substrate shown inFIG. 1, with exemplary embodiments of support structures according tothe present invention on the active surfaces thereof.

FIG. 3 is a cross-section taken along line 3-3 of FIG. 2, depicting afirst example of the manner in which the outer periphery of the supportstructure may be associated with an outer peripheral edge of thesemiconductor substrate;

FIGS. 4A through 4D are cross-sections that are also taken along line3-3 of FIG. 2, illustrating second and third examples of the manner inwhich the outer periphery of the support structure may be associatedwith an outer peripheral edge of the semiconductor substrate;

FIG. 5 is a partial top view of the semiconductor substrate shown inFIG. 1, depicting a variation of the support structure which includes aseries of concentrically positioned upwardly protruding members, each ofwhich extends along the full extent (e.g., length, circumference, etc.)of the support structure;

FIG. 6 is a cross-section taken along line 6-6 of FIG. 5;

FIG. 7 is a top view of the substrate shown in FIG. 1, illustratinganother exemplary embodiment of support structure that incorporatesteachings of the present invention;

FIG. 8 is an enlarged, partial cross-section taken along line 8-8 ofFIG. 7, showing a first example of the manner in which the outerperiphery of the support structure may be associated with an outerperipheral edge of the semiconductor substrate;

FIG. 9 is also an enlarged, partial cross-section taken along line 8-8of FIG. 7, showing a second example of the manner in which the outerperiphery of the support structure may be associated with an outerperipheral edge of the semiconductor substrate;

FIG. 10 is a schematic representation of an example of a layeredmanufacturing (e.g., stereolithography) apparatus that may be used tofabricate a support structure of the present invention upon an activesurface of a semiconductor substrate;

FIGS. 11A through 11E schematically depict use of the apparatus of FIG.10 to fabricate the support structure shown in FIG. 4 upon the activesurface of a semiconductor substrate;

FIGS. 12A and 12B schematically depict use of molding processes to forma support structure (e.g., that shown in FIG. 3) on the active surfaceof a semiconductor substrate;

FIGS. 13A and 13B schematically depict lamination of a preformedmaterial film to the active surface of a semiconductor substrate and useof subtractive processes to remove material of the preformed film and tothereby form a support structure therefrom;

FIGS. 14A and 14B are schematic representations depicting thinning of asemiconductor substrate that has a support structure of the presentinvention secured to an active surface thereof;

FIG. 15 is a schematic representation of a method for transporting athinned semiconductor substrate in accordance with teachings of thepresent invention;

FIG. 16 schematically depicts processing of a semiconductor substratefollowing thinning thereof; and

FIGS. 17A through 17C are schematic representations of a method forremoving a support structure of the present invention from a thinnedsemiconductor substrate.

DETAILED DESCRIPTION

An example of a semiconductor substrate 10 is shown in FIG. 1. Asillustrated, semiconductor substrate 10 may comprise a wafer of asemiconductor material, such as silicon, gallium arsenide, or indiumphosphide.

Semiconductor substrate 10 includes two opposite major surfaces, one ofwhich is commonly referred to in the art as an “active surface” 12 andthe other of which is typically referred to in the art as a “back side”16 (see FIGS. 3, 4A, 4B, 6, 8, and 9). Both active surface 12 and backside 16 are bounded by an outer peripheral edge 18 of semiconductorsubstrate 10. When semiconductor substrate 10 comprises a full wafer, asin the depicted example, outer peripheral edge 18 forms thecircumference of the wafer.

An edge bead removal area 20 may be located on active surface 12,adjacent to outer peripheral edge 18. Edge bead removal area 20 is arelatively narrow feature (e.g., three millimeters across) which mayextend around the entire outer periphery of semiconductor substrate 10.Notably, processing of semiconductor substrates 10 which lack edge beadremoval areas 20 is also within the scope of the present invention,although not specifically depicted in the drawings.

Within the interior of edge bead removal area 20 or, if a semiconductorsubstrate 10 lacks an edge bead removal area 20, of outer peripheraledge 18, at an interior section 22 of active surface 12, semiconductorsubstrate 10 may include a plurality of semiconductor devices 24.Adjacent semiconductor devices 24 are separated from one another bystreets 30, which extend across interior section 22 of active surface12, such as in the illustrated grid-like configuration. At least some ofthe semiconductor devices 24 that are located adjacent to outerperipheral edge 18 of semiconductor substrate 10 comprise only blanks 24p, while semiconductor devices 24 f are located somewhat internally fromouter peripheral edge 18.

Alternatively, although not shown in the drawings, semiconductorsubstrate 10 may lack semiconductor devices 24 on interior section 22 ofactive surface 12 thereof. This is because it may be desirable to thin asemiconductor substrate 10 prior to fabricating structures, such assemiconductor devices, thereon or therefrom. For example, the loss ofsemiconductor devices and the expenses incurred in fabricating the samemay be avoided if a thinned semiconductor substrate 10″ (FIG. 14B)without any semiconductor devices thereon breaks or is otherwise damagedduring the thinning process. Alternatively, one entity may thinsemiconductor substrates 10, then provide the thinned semiconductorsubstrates 10″ to one or more other entities for further processing(e.g., device fabrication).

In the illustrated examples, each semiconductor device 24 includes oneor more bond pads 27 (FIGS. 8 and 9), which facilitate electricalcommunication with integrated circuitry of that semiconductor device 24.

Turning now to FIGS. 2 through 4B, an example of a support structureaccording to the present invention, in this case a support ring 40, 40′,40 a′, 40 b′, 40 c′ (shown in FIGS. 3, 4A, 4B, 4C, and 4D, respectively)is depicted. As shown, support ring 40, 40′, 40 a′, 40 b′, 40 c′ ispositioned on active surface 12 of semiconductor substrate 10, over edgebead removal area 20 thereof. Support ring 40, 40′, 40 a′, 40 b′, 40 c′extends completely around an outer periphery 13 of active surface 12.

An outer peripheral edge 42, 42′ of support ring 40, 40′, 40 a′, 40 b′,40 c′ is in substantial alignment with (FIG. 3) or is located outside(FIGS. 4A and 4B) of outer peripheral edge 18. An interior edge 44 ofsupport ring 40, 40′, 40 a′, 40 b′, 40 c′ defines surfaces of anaperture 45 through support ring 40, 40′, 40 a′, 40 b′, 40 c′. Interiorsection 22 of active surface 12 and, thus, all of the semiconductordevices 24 f thereon are completely surrounded by interior edge 44 ofsupport ring 40, 40′, 40 a′, 40 b′, 40 c′ and exposed through aperture45 thereof.

Support ring 40, 40′, 40 a′, 40 b′, 40 c′ is formed from a material thatis compatible with the material or materials of semiconductor substrate10. The material of support ring 40, 40′, 40 a′, 40 b′, 40 c′ will,along with the thickness of support ring 40, 40′, 40 a′, 40 b′, 40 c′,impart a thinned semiconductor substrate 10″ (FIG. 14B) with the desiredamount of rigidity. For example, it may be desirable to impart a thinnedsemiconductor substrate 10″ with approximately the same amount ofrigidity as that of the semiconductor substrate 10 prior to thinningthereof. As another example, it may be desirable to impart a thinnedsemiconductor substrate 10″ with sufficient rigidity to prevent bending,sagging, or other nonplanarity thereof during processing ortransportation thereof following the thinning process.

In addition, the material from which support ring 40, 40′, 40 a′, 40 b′,40 c′ is formed may be substantially impervious to chemicals (e.g., wetand dry etchants) that may be used in backgrinding processes, as well ascompatible with conditions of any post-thinning processes.

The material from which support ring 40, 40′, 40 a′, 40 b′, 40 c′ isformed may also facilitate or enhance sealing of support ring 40, 40′,40 a′, 40 b′, 40 c′ to a support structure, such as a vacuum chuck, assemiconductor substrate 10 is being thinned or otherwise processed.

It is also desirable to form support ring 40, 40′, 40 a′, 40 b′, 40 c′from a material that has a coefficient of thermal expansion (CTE) thatis as close as possible to that of the material or materials from whichsemiconductor substrate 10 is formed (e.g., silicon has a CTE of about2.9×10⁻⁶/° C.), thereby preventing warpage of semiconductor substrate 10and delamination of support ring 40, 40′, 40 a′, 40 b′, 40 c′ therefromduring processing of semiconductor substrate 10 (e.g., thinning or anyprocessing that occurs thereafter).

Exemplary materials that may be used to form support ring 40, 40′, 40a′, 40 b′, 40 c′ include consolidatable materials that are useful inlayered manufacturing processes (e.g., photoimageable polymers that areuseful in stereolithography processes), photoresists, thermoset polymers(e.g., moldable silicones), and the like. While many of these materialsmay be less rigid than desired or have CTEs which differ significantlyfrom the material or materials of semiconductor substrate 10, fillersmay be added thereto to impart the materials and, thus, support ring 40,40′, 40 a′, 40 b′, 40 c′ with the desired properties. Examples offillers that may be used with any of the foregoing materials include,but are not limited to, silica (i.e., glass, silicon) particles, alumina(i.e., ceramic) particles, nitride (e.g., silicon nitride, boronnitride) particles, and polymeric particles or fibers (e.g.,poly(p-phenyleneterephtalamide) fibers, which are marketed under thetradename KEVLAR® by E.I. du Pont de Nemours & Company of Wilmington,Del.). Photoimageable polymers that are useful in stereolithographyprocesses may have CTEs of about 55×10⁻⁶/° C. When a silica fillermaterial is included therein, with the mixture including about 50%, byweight, photoimageable polymer and about 50%, by weight, silicaparticles, the CTE of the mixture is lowered significantly, to about32×10⁻⁶/° C. Fillers may also increase or enhance the fracture toughness(e.g., KEVLAR®), strength, rigidity, thermal properties (e.g., boronnitride), or structural integrity of the material (e.g., photoimageablepolymer, photoresist, thermoset polymer, etc.) within which they aremixed.

Along with the materials from which support ring 40, 40′, 40 a′, 40 b′,40 c′ is formed, the dimensions or configuration thereof may provide thedesired properties. For example, as illustrated in FIGS. 3 through 4D, asupport ring 40, 40′, 40 a′, 40 b′, 40 c′ according to the presentinvention may have a width W which is at least as great as the width ofedge bead removal area 20 (i.e., typically about 3 mm or more).

In another example, with continued reference to FIGS. 3 through 4D, theheight H of support ring 40, 40′, 40 a′, 40 b′, 40 c′ may impart supportring 40, 40′, 40 a′, 40 b′, 40 c′ and, thus, a thinned semiconductorsubstrate 10″ (FIG. 14B) with which support ring 40, 40′, 40 a′, 40 b′,40 c′ is to be used with a desired amount of rigidity. For example,depending, of course, upon the rigidity and CTE of the material fromwhich support ring 40, 40′, 40 a′, 40 b′, 40 c′ is formed, support ring40, 40′, 40 a′, 40 b′, 40 c′ may have a height of as small as about 25μm (one mil) to about 200 μm (eight mils) or greater.

When a thinned semiconductor substrate 10″ and a support ring 40, 40′,40 a′, 40 b′, 40 c′ thereon will be handled or processed with equipmentwhich is configured to handle and process semiconductor substrates ofstandard diameters and thicknesses, the combined height H of supportring 40, 40′, 40 a′, 40 b′, 40 c′ and thickness of a thinnedsemiconductor substrate 10″ (FIG. 14B) should not exceed the maximumsubstrate thickness (e.g., about 800 μm) that such equipment isconfigured to accommodate. Likewise, the outer diameter (OD) of supportring 40, 40′, 40 a′, 40 b′, 40 c′ should not exceed the maximumsubstrate diameter (e.g., 200 mm, 300 mm, etc.) that equipment forhandling or processing a thinned semiconductor substrate 10″ may beconfigured to accommodate.

As shown in FIG. 3, an outer peripheral edge 42 of support ring 40 maybe substantially coextensive and, thus, in substantial alignment with anouter peripheral edge 18 of semiconductor substrate 10.

Alternatively, as depicted in FIG. 4A, a support ring 40′ may extendbeyond outer peripheral edge 18 of semiconductor substrate 10, with anouter peripheral edge 42′ of a support ring 40′ being positioned outsideof outer peripheral edge 18 of semiconductor substrate 10. Accordingly,support ring 40′ includes an overhang region 46′, which is locatedbeyond outer peripheral edge 18 of semiconductor substrate 10.

In addition, support ring 40′ may include a circumferential supportelement 48′ beneath overhang region 46′, substantially coplanar withsemiconductor substrate 10, and in substantial contact with outerperipheral edge 18. Circumferential support element 48′ may have aheight which is about the same as or less than the desired thickness ofsemiconductor substrate 10 following thinning thereof (i.e., thethickness of thinned semiconductor substrate 10″ (FIG. 14B).

Overhang region 46′ of support ring 40′ or a variation thereof mayinclude one or more ancillary features, such as one or more markings,locating features, or fixturing features. By way of example only, one ormore dowel holes 55, slots 56, or fiducial marks 57 may be formed on,in, or through overhang region 46′, as shown in FIG. 2A.

The support ring 40 a′ shown in FIG. 4B includes all of the features ofsupport ring 40′, except for circumferential support element 48′ (FIG.4A).

Shown in FIG. 4C is another variation of support ring 40 b′, whichincludes all of the features of support ring 40′ (FIG. 4A). Support ring40 b′ differs from support ring 40′ in that circumferential supportelement 48 b′ of support ring 40 b′ extends from overhang region 46′substantially to, as shown, or beyond a plane in which back side 16 ofsemiconductor substrate 10 is located.

Once a semiconductor substrate 10 with a support ring 40 b′ thereon hasbeen thinned (e.g., by chemical thinning or polishing processes),circumferential support element 48 b′ will protrude beyond back side 16,forming a lip (not shown) that extends completely around outerperipheral edge 18 at back side 16. Such a lip may be useful forenhancing the rigidity of the thinned semiconductor substrate 10″ (seeFIG. 14B), as well as for sealing back side 16 against a carrier whileprocessing is being effected over active surface 12 of thinnedsemiconductor substrate 10″.

FIG. 4D illustrates still another variation of support ring 40 c′, whichincludes an overhang region 46′ and a circumferential support element 48c′. Circumferential support element 48 c′ differs from circumferentialsupport element 48′ (FIG. 4A) in that circumferential support element 48c′ extends from overhang region 46′ to a location beyond a plane inwhich back side 16 of semiconductor substrate 10 is located. Inaddition, circumferential support element 48 c′ is spaced apart fromouter peripheral edge 18 of semiconductor substrate 10, providing a gapG that accommodates expansion or contraction of support ring 40 c′ orsemiconductor substrate 10 due to CTE mismatch therebetween. Due to thepresence of gap G, support ring 40 c′ also includes a retention ledge49′ that extends inwardly from a lower edge of circumferential supportelement 48 c′, along a plane which is parallel to a plane in which backside 16 of semiconductor substrate 10 is located, and over at least aperipheral portion 17 of back side 16, thereby trapping outer peripheraledge 18.

As shown in FIGS. 5 and 6, another variation of support ring 40″ maycomprise one or more sealing elements 50″ which protrude from an uppersurface 49″ of support ring 40″. FIGS. 5 and 6 depict support ring 40″as including three concentrically arranged sealing elements 50″,although support rings 40″ with other numbers (i.e., as few as one ormore than three) of sealing elements 50″ are also within the scope ofthe present invention. Sealing elements 50″ are somewhat compliantfeatures that are configured to facilitate the creation of a sealbetween upper surface 49″ of support ring 40″ and a surface or feature(not shown) against which support ring 40″ is to be positioned, such asa surface of a sealing ring of a vacuum chuck.

Features of other embodiments of support structures according to thepresent invention, which are referred to herein as “support members”140, 140′, are pictured in FIGS. 7 through 9. In addition to includingan outer peripheral portion 150, 150′ that covers an edge bead removalarea 20 of active surface 12 of semiconductor substrate 10, supportmember 140, 140′ also includes an interior portion 160, 160′ that formsprotective structures 28, 28′ over semiconductor devices 24 f that arecarried by interior section 22 of active surface 12.

As FIGS. 8 and 9 illustrate, outer peripheral portion 150, 150′ ofsupport member 140, 140′ may be configured substantially the same assupport rings 40, 40′ depicted in FIGS. 3 and 4A, respectively. Inaddition, although not illustrated, outer peripheral portion 150, 150′of support member 140, 140′ may include one or more sealing elements,such as the sealing elements 50″ that are shown in FIGS. 5 and 6.

With continued reference to FIGS. 8 and 9, each protective structure 28,28′ of interior portion 160, 160′ of support member 140, 140′ includesat least one aperture 162, 162′ through which a corresponding bond pad27 of the corresponding, underlying semiconductor device 24 f isexposed.

FIG. 9 shows a semiconductor substrate 10′ which includes trenches 32 atthe locations of streets 30, material of streets 30 having been removedby known processes, such as partial cutting with a wafer saw,photolithography (e.g., mask) and etch processes, or the like, to formtrenches 32. Thus, protective structure 28′ covers an active surface 26of each corresponding semiconductor device 24 f, as well as at least aportion of peripheral edges 25 thereof.

No material has been removed from streets 30 of the semiconductorsubstrate 10 shown in FIG. 8. Accordingly, an alternative configurationof the protective structure 28′ that is shown in FIG. 8 covers only theactive surface 26 of a semiconductor device 24 f, not any portions ofthe peripheral edges 25 thereof.

Like support rings 40, 40′, 40 a′, 40 b′, 40 c′, 40″, support members140, 140′ may be formed from a material which provides the desireddegrees of rigidity and sealability. The thickness and other dimensionsof support members 140, 140′ may also factor into the rigiditiesthereof.

In addition, since support members 140, 140′ include protectivestructures 28, 28′, the material from which support members 140, 140′also provides other desirable properties, such as a particular level ofelectrical insulation, an ability to withstand subsequent processingconditions (e.g., dicing, further packaging, etc.), an ability towithstand operating conditions (e.g., temperature) to which eachsemiconductor device 24 f is subjected when in use, a particular degreeof impermeability to moisture, or the like.

Turning now to FIGS. 10 through 13B, various exemplary methods forforming support structures, including support rings 40, 40′, 40″ andsupport members 140, 140′, are depicted. Although the description ofthese processes herein is limited to forming of a support ring 40′(FIGS. 11A through 12C) or a support ring 40 (FIGS. 13A and 13B), theyare also useful for forming other embodiments of support structures thatincorporate teachings of the present invention.

FIGS. 10 and 11A through 11E show a layered manufacturing process thatmay be used to form a support ring 40′.

In FIG. 10, an example of a stereolithography system 1000, which effectsa type of layered manufacturing process that employs selectiveirradiation of radiation-curable (e.g., by ultraviolet light, etc.)curable resin, is schematically represented.

Stereolithography system 1000 includes a fabrication tank 1100 and amaterial consolidation system 1200, a machine vision system 1300, acleaning component 1400, and a material reclamation system 1500 that areassociated with fabrication tank 1100. The depicted stereolithographysystem 1000 also includes a substrate handling system 1600, such as arotary feed system or linear feed system available from GenmarkAutomation Inc. of Sunnyvale, Calif., for moving fabrication substrates(e.g., semiconductor substrates 10) from one system of stereolithographysystem 1000 to another. Features of one or more of the foregoing systemsmay be associated with one or more controllers 1700, such as computerprocessors or smaller groups of logic circuits, in such a way as toeffect their operation in a desired manner.

Controller 1700 may comprise a computer or a computer processor, such asa so-called “microprocessor,” which may be programmed to effect a numberof different functions. Alternatively, controller 1700 may be programmedto effect a specific set of related functions or even a single function.Each controller 1700 of stereolithography system 1000 may be associatedwith a single system thereof or a plurality of systems so as toorchestrate the operation of such systems relative to one another.

Fabrication tank 1100 includes a chamber 1110 which is configured tocontain a support system 1130. In turn, support system 1130 isconfigured to carry one or more semiconductor substrates 10.

Fabrication tank 1100 may also have a reservoir 1120 associatedtherewith. Reservoir 1120 may be continuous with chamber 1110.Alternatively, reservoir 1120 may be separate from; but communicate withchamber 1110 in such a way as to provide unconsolidated material 1126thereto. Reservoir 1120 is configured to at least partially contain avolume 1124 of unconsolidated material 1126, such as a photoimageablepolymer, or “photopolymer,” particles of thermoplastic polymer,resin-coated particles, or the like.

Photopolymers believed to be suitable for use with a stereolithographysystem 1000 and for fabricating support structures, such as supportrings 40′, in accordance with teachings of the present invention,include, without limitation, Cibatool SL 5170, SL 5210, SL 5530, and SL7510 resins. All of these photopolymers are available from CibaSpecialty Chemicals Inc. of Basel, Switzerland.

Reservoir 1120 or another component associated with one or both offabrication tank 1100 and reservoir 1120 thereof may be configured tomaintain a surface 1128 of a portion of volume 1124 located withinchamber 1110 at a substantially constant elevation relative to chamber1110.

A material consolidation system 1200 is associated with fabrication tank1100 in such a way as to direct consolidating energy 1220 into chamber1110 thereof, toward at least areas of surface 1128 of volume 1124 ofunconsolidated material 1126 within reservoir 1120 that are located oversemiconductor substrate 10. Consolidating energy 1220 may comprise, forexample, electromagnetic radiation of a selected wavelength or a rangeof wavelengths, an electron beam, or other suitable energy forconsolidating unconsolidated material 1126. Material consolidationsystem 1200 includes a source 1210 of consolidating energy 1220. Ifconsolidating energy 1220 is focused, source 1210 or a location controlelement 1212 associated therewith (e.g., a set of galvanometers ormirrors, including one for x-axis movement and another for y-axismovement) may be configured to direct, or position, consolidating energy1220 toward a plurality of desired areas of surface 1128. Alternatively,if consolidating energy 1220 remains relatively unfocused, it may bedirected generally toward surface 1128 from a single, fixed location orfrom a plurality of different locations. In any event, operation ofsource 1210, as well as movement thereof, if any, may be effected underthe direction of controller 1700.

When material consolidation system 1200 directs focused consolidatingenergy 1220 toward surface 1128 of volume 1124 of unconsolidatedmaterial 1126, stereolithography system 1000 may also include a machinevision system 1300. Machine vision system 1300 facilitates the directionof focused consolidating energy 1220 toward desired locations offeatures on semiconductor substrate 10. As with material consolidationsystem 1200, operation of machine vision system 1300 may be proscribedby controller 1700. If any portion of machine vision system 1300, suchas a camera 1310 thereof, moves relative to chamber 1110 of fabricationtank 1100, that portion of machine vision system 1300 may be positionedso as provide a clear path to all of the locations of surface 1128 thatare located over each semiconductor substrate 10 within chamber 1110.

Optionally, one or both of material consolidation system 1200 (which mayinclude a plurality of mirrors 1214) and machine vision system 1300 maybe oriented and configured to operate in association with a plurality offabrication tanks 1100. Of course, one or more controllers 1700 would beuseful for orchestrating the operation of material consolidation system1200, machine vision system 1300, and substrate handling system 1600relative to a plurality of fabrication tanks 1100.

Cleaning component 1400 of stereolithography system 1000 may alsooperate under the direction of controller 1700. Cleaning component 1400of stereolithography system 1000 may be continuous with chamber 1110 offabrication tank 1100 or positioned adjacent to fabrication tank 1100.If cleaning component 1400 is continuous with chamber 1110, anyunconsolidated material 1126 that remains on a semiconductor substrate10 may be removed therefrom prior to introduction of anothersemiconductor substrate 10 into chamber 1110.

If cleaning component 1400 is positioned adjacent to fabrication tank1100, residual unconsolidated material 1126 may be removed from asemiconductor substrate 10 as semiconductor substrate 10 is removed fromchamber 1110. Alternatively, any unconsolidated material 1126 remainingon semiconductor substrate 10 may be removed therefrom aftersemiconductor substrate 10 has been removed from chamber 1110, in whichcase the cleaning process may occur as another semiconductor substrate10 is positioned within chamber 1110.

Material reclamation system 1500 collects excess unconsolidated material1126 that has been removed from a semiconductor substrate 10 by cleaningcomponent 1400, then returns the excess unconsolidated material 1126 toreservoir 1120 associated with fabrication tank 1100.

In use, controller 1700, under control of computer-aided drafting (CAD)or stereolithography (.stl) programming, may orchestrate operation ofvarious components of stereolithography system 1000 to fabricate supportstructures, such as support rings 40′, as well as other features.

FIGS. 11A through 11E depict an example of the manner in which a supportstructure, such as support ring 40′, may be fabricated.

With reference to FIG. 11A, semiconductor substrate 10 is positioned ona support platen 1112 within chamber 1110 of fabrication tank 1100 (FIG.10). As depicted, semiconductor substrate 10 is submerged within volume1124 of unconsolidated material 1126 so that unconsolidated material1126 covers and fills all of the features that are located at activesurface 12 of semiconductor substrate 10.

Next, as shown in FIG. 11B, support platen 1112 is raised such that theupper surface of semiconductor substrate 10 is brought to about the samelevel as (i.e., coplanar with) surface 1128, as shown, or above surface1128 of volume 1124. Areas 1129 of unconsolidated material 1126 that arelocated adjacent to outer peripheral edge 18 of semiconductor substrate10 are then at least partially selectively consolidated (e.g., with alaser or other focused consolidating energy 1220) to initiate theformation of circumferential support element 48′ (FIGS. 4A and 11C) ofsupport ring 40′ (FIG. 4A). This process may be effected once ifcircumferential support element 48′ comprises a single material layer,or repeated multiple times, lowering semiconductor substrate 10 inmultiple increments until active surface 12 thereof is substantiallyplanar with surface 1128 of volume 1124, if circumferential supportelement 48′ includes a plurality of superimposed, contiguous, mutuallyadhered layers of material.

Once circumferential support element 48′ has been formed, portions ofsupport ring 40′ which are located above the plane in which activesurface 12 of semiconductor substrate 10 is located, including overhangregion 46′ thereof, may be fabricated, as shown in FIG. 11C. Supportplaten 1112 is lowered such that active surface 12 is submerged beneathsurface 1128 of volume 1124 a distance that, considering any change inthe density of unconsolidated material 1126 upon consolidation thereof,will result in a layer or sublayer of consolidated material thatprotrudes above active surface 12 a desired height (e.g., about one mil,about four mils, about eight mils, etc.). Unconsolidated material 1126at locations where the fabrication of a support structure, such assupport ring 40′, is desired may then be selectively consolidated withfocused consolidating energy 1220 (e.g., a laser beam) to form at leastanother layer of support ring 40′.

As illustrated in FIG. 11D, these processes may be repeated a number oftimes until a support structure, such as support ring 40′, and featuresthereof (e.g., the sealing elements 50″ shown in FIGS. 5 and 6, whichmay be formed as one or more separate layers from the remainder ofsupport ring 40′) have been completely formed.

Following the fabrication of a support structure, such as support ring40′, on semiconductor substrate 10, support platen 1112 may be raisedsuch that at least semiconductor substrate 10 and the support structure(e.g., support ring 40′) carried thereby are removed from volume 1124 ofunconsolidated material 1126, as shown in FIG. 11E. Thereafter,semiconductor substrate 10 and the support structure thereon may becleaned, as known in the art.

Alternatively, a support structure according to the present inventionmay be formed by applying a photoresist (e.g., by spin-on processes orotherwise, as known in the art) onto active surface 12 of semiconductorsubstrate 10 (FIG. 1), then exposing desired regions of the photoresistto one or more suitable wavelengths of radiation (e.g., through areticle), as in known photolithography processes, and developing theexposed regions with a chemical or chemicals that are suitable forconsolidating the photoresist that has been exposed.

Referring now to FIGS. 12A and 12B, an exemplary process for molding asupport structure, such as a support ring 40′ (FIGS. 4A and 12B) inplace upon a semiconductor substrate 10 is depicted.

As shown in FIG. 12A, semiconductor substrate 10 is positioned within asupport cavity 212 of or otherwise supported by a first half 210 of amold 200, with active surface 12 of semiconductor substrate 10 remainingexposed. Thereafter, a second half 220 of mold 200 is then positionedover active surface 12. Regions of active surface 12, including edgebead removal area 20 thereof, upon which the support structure (e.g.,support ring 40′) is to be positioned, communicate with one or morecavities 222 of second half 220. Of course, first and second halves 210,220 of mold 200 may include other features (e.g., runners, vents, etc.)that are positioned appropriately for the type of molding process inwhich mold 200 is to be used.

Once semiconductor substrate 10 has been properly positioned within mold200, known mold processes (e.g., transfer molding, pot molding,injection molding, etc.) may be used to introduce liquid mold materialfrom which the support structure (e.g., support ring 40′) is to beformed into each cavity 222 and onto regions of active surface 12 thatcommunicate with each cavity 222.

As shown in FIG. 12B, once the mold material has sufficiently hardened(e.g., cured, cooled, etc.), semiconductor substrate 10 and the supportstructure (e.g., support ring 40′) that has been molded in place thereonmay be removed from mold 200, as known in the art.

Another exemplary process for forming a support structure, such assupport ring 40′ on at least an active surface 12 of a semiconductorsubstrate 10 is pictured in FIGS. 13A and 13B.

In FIG. 13A, a preformed sheet 300 of a material from which a supportstructure, such as support ring 40 (FIG. 2), is to be formed ispositioned over and secured to active surface 12 of semiconductorsubstrate 10. Preformed sheet 300 may be secured to active surface 12 byany technique which is compatible with the material of preformed sheet300 and with semiconductor substrate 10 and semiconductor devices 24(FIGS. 1 and 2) that have been fabricated on active surface 12 thereof.By way of nonlimiting example, preformed sheet 300 may be secured toactive surface 12 with a pressure-sensitive or curable adhesive, byheating preformed sheet 300 or active surface 12, by applying solvent toat least a lower surface 302 of preformed sheet 300 or to active surface12, or by any other suitable process known in the art.

Once preformed sheet 300 has been laminated to active surface 12,subtractive processes may be used to form a support structure accordingto the present invention therefrom, as shown in FIG. 13B. For example,and not to limit the scope of the present invention, a support structure(e.g., support ring 40) may be formed by the use of photolithographyprocesses to form a mask 310 and removal of material through apertures312 in mask 310 (e.g., with an etchant or solvent that is suitable foruse in removing the material of preformed sheet 300), photoablation(e.g., which is useful with polymer films), or otherwise, as known inthe art and suitable for use with the material of preformed sheet 300and with semiconductor substrate 10 and semiconductor devices 24 (FIGS.1 and 2) that have been fabricated on active surface 12 thereof. Mask310 may then be removed by way of known resist strip processes.

Of course, combinations of processes for forming support structures thatincorporate teachings of the present invention are also within the scopeof the present invention. For example, a support ring 40, 40′, 40 a′, 40b′, 40 c′, 40″ may be formed separately from a semiconductor substrate10 (FIG. 1), in one or more pieces (e.g., support ring 40 c′ may beformed in two or more pieces), then assembled with semiconductorsubstrate 10 (and, in the case of support ring 40 c′, pieces areassembled with one another) and secured (i.e., adhered) thereto (and, inthe case of support ring 40 c′, secured to one another), such as bystereolithography processes or with an uncured polymer (e.g., thermosetpolymer or photopolymer) which is subsequently cured by exposure toradiation or heat.

Turning now to FIGS. 14A and 14B, thinning of back side 16 ofsemiconductor substrate 10 is schematically depicted. Although FIGS. 14Aand 14B illustrate backgrinding of a semiconductor substrate 10 thatincludes a support ring 40 on at least active surface 12 thereof,backgrinding may also be effected with another embodiment of supportstructure of the present invention on at least active surface 12, aswell as with another embodiment of semiconductor substrate (e.g.,semiconductor substrate 10′, shown in FIG. 9).

As shown in FIG. 14A, semiconductor substrate 10 is positioned activesurface 12-down over a carrier 400, for example, a vacuum chuckavailable from Semitool, Inc. of Kalispell, Mont. The support structure(e.g., support ring 40) on active surface 12 of semiconductor substrate10 contacts a surface 410 of carrier 400 or a corresponding feature(e.g., an O-ring 412) thereon, and may form a seal thereagainst. Knownprocesses (e.g., application of a negative pressure N to active surface12 of semiconductor substrate 10) may be used to secure semiconductorsubstrate 10 against surface 410 or a feature (e.g., o-ring 412) thereonand, optionally, to seal active surface 12 from exposure to conditionsthat are present at the exterior (e.g., back side 16 and outerperipheral edge 18) of semiconductor substrate 10.

Once semiconductor substrate 10 has been secured to carrier 400, knowntechniques may be used to remove material from back side 16 ofsemiconductor substrate 10 and, thus, to thin semiconductor substrate 10to a desired thickness, as depicted in FIG. 14B. By way of example only,known mechanical backgrinding or polishing processes (e.g., mechanicallapping techniques), chemical backgrinding or polishing processes (e.g.,wet etch processes, dry etch processes, such as that described in U.S.Pat. No. 6,498,074 to Siniaguine et al., the disclosure of which ishereby incorporated herein in its entirety by this reference, etc.), ora combination of mechanical and chemical backgrinding or polishingprocesses may be employed to thin semiconductor substrate 10. Suchthinning processes may be effected until the resulting thinnedsemiconductor substrate 10″ has a desired thickness (e.g., a thicknessof about 230 μm or less, a thickness of about 50 μm or less, etc.).

A thinned semiconductor substrate 10″, which includes a supportstructure, such as support ring 40, on at least active surface 12thereof, is shown in FIG. 14B.

FIG. 15 schematically depicts thinned semiconductor substrates 10″ ofthe present invention in substrate cartridges 510 of a multi-substratecassette 500. As shown, cassette 500 includes a plurality of substratecartridges 510, each of which is somewhat horizontally oriented andconfigured to receive a semiconductor substrate of standard dimensions(e.g., a 200 mm or 300 mm silicon wafer that has not been thinned).Substrates, including thinned semiconductor substrates 10″ thatincorporate teachings of the present invention, may be introduced intoand removed from substrate cartridges 510, as known in the art (e.g.,with robotic handling equipment).

Once one or more thinned semiconductor substrates 10″ have beenpositioned within substrate cartridges 510 of cassette 500, they may betransported from process equipment in which backgrinding or thinning iseffected to equipment by which thinned semiconductor substrates 10″ willbe further processed.

For example, thinned semiconductor substrates 10″, such as those formedin accordance with teachings of the present invention, may be secured(e.g., with adhesive materials) to other substrates, such as insulatorslike ceramic, glass, or sapphire, to form silicon-on-insulator (SOI)type substrates, such as a silicon-on-ceramic (SOC), silicon-on-glass(SOG), silicon-on-sapphire (SOS), or similar substrates.

As another example, as shown in FIG. 16, semiconductor devices 24 f thatare carried by active surface 12 of a thinned semiconductor substrate10″ may be packaged by known wafer level packaging (WLP) processes(e.g., by stereolithography, by use of known layer formation andpatterning processes, etc.), which typically include the formation ofprotective structures 28″ over each semiconductor device 24 f.

FIGS. 17A through 17C are schematic representations of a method forremoving a support structure of the present invention, such as a supportring 40, 40′, 40 a′, 40 b′, 40 c′, 40″, as shown in FIG. 17A, a supportmember 140, as shown in FIG. 17B, or a support member 140′, as shown inFIG. 17C, from a thinned semiconductor substrate 10″.

As shown in FIG. 17A, known dicing processes (e.g., the depicted wafersaw 600, a laser, etc.) may be used to singulate semiconductor devices24 f from thinned semiconductor substrate 10″. Since support ring 40,40′, 40″ does not cover any of the semiconductor devices 24 f that arecarried by active surface 12′ of thinned semiconductor substrate 10″,support ring 40, 40′, 40″ will remain on the fragments 124 p′ thatresult from the dicing process, with each of the resulting semiconductordice 124′ being substantially bare (e.g., active surfaces 12′ thereofremaining exposed).

Referring now to FIG. 17B, when the support structure comprises asupport structure (e.g., support member 140) that includes an interiorportion (e.g., interior portion 160) that covers portions of the activesurfaces 12′ of semiconductor devices 24 f, dicing, or singulation, ofthe semiconductor devices 24 f from one another proceeds through boththe interior portion and thinned semiconductor substrate 10″. The resultof such dicing, or singulation, is a plurality of low-profile packagedsemiconductor devices 123′.

FIG. 17C illustrates dicing, or singulation, of a thinned semiconductorsubstrate 10′ that includes trenches 32 along streets 30 betweenadjacent semiconductor devices 24 f as well as a support member 140′substantially covering active surfaces 12′ thereof. As shown, during thethinning process, trenches 32 and material of protective structures 28′may be exposed through back side 16 of semiconductor substrate 10′,effectively separating semiconductor devices 24 f from one another.Nonetheless, protective structures 28′, which comprise portions ofinterior portion 160′ of support member 140′, remain connected to oneanother, preventing the physical separation of semiconductor devices 24f from each another. Support member 140′ may be diced, or singulated, asknown in the art, such as by use of the illustrated wafer saw 600. Whenthe blade or blades 602 of wafer saw 600 are narrower than the distanceacross trenches 32, peripheral edges 125 of each singulatedsemiconductor die 124′ will be at least partially covered withperipheral portions 129′ of singulated protective structures 128′, eachof these elements together forming a low-profile packaged semiconductordevice 123′.

Once semiconductor devices 24 f (FIGS. 17A through 17C) have beenphysically separated from one another, further processing may occur,such as the selection of known good dice (KGDs), the connection thereofto one or more other semiconductor device components (e.g., a carriersubstrate, an interposer, another semiconductor device, etc.), theincorporation thereof into a stacked multi-chip module (MCM) of standarddimensions but increased chip density, or packaging thereof with one ormore other semiconductor device components may be conducted, as known inthe art.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some of the presently preferredembodiments. Similarly, other embodiments may be devised withoutdeparting from the spirit or scope of the present invention. Featuresfrom different embodiments may be employed in combination. The scope ofthe invention is, therefore, indicated and limited only by the appendedclaims and their legal equivalents rather than by the foregoingdescription. All additions, deletions and modifications to the inventionas disclosed herein which fall within the meaning and scope of theclaims are to be embraced thereby.

1. A method for thinning a semiconductor substrate, comprising: forminga support structure on an active surface of the semiconductor substratesuch that the support structure includes an outer peripheral portionthat extends beyond an outer peripheral edge of the semiconductorsubstrate and a downwardly extending portion located laterally adjacentto the outer peripheral edge of the semiconductor substrate; removingmaterial from a back side of the semiconductor substrate to form athinned semiconductor substrate; and transporting the thinnedsemiconductor substrate for further processing.
 2. The method of claim1, wherein forming the support structure comprises forming a supportring on the active surface adjacent to an outer peripheral edge of thesemiconductor substrate.
 3. The method of claim 2, wherein forming thesupport ring comprises forming the support ring such that eachsemiconductor device that has been fabricated on the active surface islocated within an inner periphery of the support ring and is exposedtherethrough.
 4. The method of claim 1, wherein forming the supportstructure includes forming a layer of packaging material over the activesurface and extending radially outward to at least an outer peripheraledge of the semiconductor substrate.
 5. The method of claim 1, whereinforming the support structure comprises: forming a layer comprisingunconsolidated material over at least an outer peripheral portion of theactive surface; and at least partially consolidating the unconsolidatedmaterial within at least outer peripheral regions of the layer.
 6. Themethod of claim 5, wherein at least partially consolidated theunconsolidated material comprises directing a focused energy beam ontoat least the outer peripheral regions of the layer.
 7. The method ofclaim 6, wherein directing the focused energy beam comprises directing alaser beam onto at least the outer peripheral regions of the layer. 8.The method of claim 1, wherein forming the support structure comprisesstereolithographically forming the support structure.
 9. The method ofclaim 1, wherein forming the support structure comprises: positioning apreformed film of support material over the active surface; and removingselected regions of the preformed film.
 10. The method of claim 1,wherein forming the support structure comprises molding the supportstructure on the active surface.
 11. The method of claim 1, furthercomprising: securing the semiconductor substrate to a platen with theactive surface facing the platen and the support structure abutting atleast one surface or feature of or on the platen.
 12. The method ofclaim 11, wherein securing the semiconductor substrate comprisesapplying a negative pressure to the active surface.
 13. The method ofclaim 11, wherein securing the semiconductor substrate includes sealingthe support structure against the at least one surface or feature. 14.The method of claim 1, wherein removing material from the back side ofthe semiconductor substrate comprises at least one of chemically andmechanically removing material from the back side.
 15. The method ofclaim 1, wherein removing material from the back side of thesemiconductor substrate comprises back grinding.
 16. The method of claim1, wherein the support structure supports the thinned semiconductorsubstrate during transporting thereof.